The current wave of 3-dimensional (3D) films is gaining popularity and made possible by the ease of use of 3D digital cinema projection systems. However, the rate of rollout of digital systems is not adequate to keep up with demand, partly because of the relatively high cost involved. Although earlier 3D film systems suffered from various technical difficulties, including mis-configuration, low brightness, and discoloration of the picture, they were considerably less expensive than the digital cinema approach. In the 1980's, a wave of 3D films were shown in the US and elsewhere, making use of a lens and filters designed and patented by Chris Condon (U.S. Pat. No. 4,464,028). Other improvements to Condon were proposed, such as by Lipton in U.S. Pat. No. 5,841,321. Subject matter in both references are herein incorporated by reference in their entireties.
One lens configuration uses a dual-lens arrangement (e.g., an upper lens for projecting images for one eye, and a lower lens for projecting images for the other eye) to simultaneously project left- and right-eye images of a stereoscopic image pairs laid out above and below each other on a same strip of film. The left- and right-eye images are encoded by passing each image through respective lens assemblies with separate filters (e.g., including polarizers or color filters). The filter in each lens assembly encodes a respective right- or left-eye image so that a viewer or audience wearing glasses having corresponding left- and right-eye decoding filters (can also be referred to as viewing filters) will only see projected left-eye images through the left-eye viewing filter, and projected right-eye images through the right-eye viewing filter.
However, the polarizers and other elements (including lenses) in these prior film-based 3D systems often suffer from overheating and failure when exposed to high radiant flux from the illumination source typically used in these systems. As a result, such projection systems must be operated at a reduced brightness, and/or with frequent replacement of one or more of the polarizers and other elements. Although some systems incorporate infrared- or ultraviolet-blocking filters in front of the projection lens or polarizers to reduce overheating, such measures are not able to completely eliminate the problem.